Color

Three color are not orthogonal, i.e. they are activated by overlapping wavelengths. [Source: https://bsky.app/profile/stein.ke/post/3ln75rrxncc2t]

Colours correspond to infinite-dimensional vectors, since there are infinitely many wavelengths of light. But humans can only perceive a three-dimensional projection of colour (red, green, & blue). What's interesting is that it's not an orthogonal projection. Here's a plot of the basis vectors.